Images captured with a digital motion camera or a video camera often have a look described as the “soap-opera” look: relatively flat images with blown-out highlights, blocked-up shadow details and harsh flesh tones. However, electronic capture has been well accepted because of the potentially cheaper economics as compared to film capture. Also, electronically captured material is usually viewed only on a television screen, which is a far less demanding output venue than a movie theater screen. Despite the cost and output venue, however, certain attributes of the film process provide an appearance which is aesthetically pleasing and, to some extent, may influence the artistic quality of the recorded images. Thus, there has always been a market for the desire to take these images captured with the “soap-opera” look and give them the appearance of film, as if they were originated on film and put through the film system (the term “filmic” will be used to mean “appearance of film”). Filmic can be used to describe images with high dynamic range, good highlight and shadow detail, pleasing flesh tones and, in general, an overall richer image than obtained from the “soap-opera” look.
Digital image processing may take place on video images, as described in U.S. Pat. Nos. 5,335,013, 5,475,425 and 5,831,673, in order to emulate the broadcast look of film or the look of film after it has been through a telecine transfer. These patents describe systems for rendering the output of a video camera to simulate the visual appearance of motion picture film that has been transferred or converted to a video signal to be output directly for television broadcasting or recording on video tape. Further, the above-cited prior art teaches three components for the emulation of the look of broadcast motion picture film. One component deals with the conversion of the video or digital material into various video formats from either 30 frames per second (fps) or 24 fps origination rate. The second component allows for the selective addition of filtered noise to the electronically captured images to give the appearance of motion picture film grain. The third component allows for the alteration of the apparent contrast of the video image so the desired broadcast film appearance may be obtained. More specifically, in the '013 patent a gray scale modifier is used as a look-up table (LUT) and the operator can choose between a variety of curves (% light level vs. video level) stored in programmable read-only memory (PROM) to reflect different film types or achieve different photographic effects. The desired curve is selected by pressing a switch on the hardware.
U.S. Pat. Nos. 5,140,414; 5,374,954; 5,406,326; 5,457,491 and 5,687,011 (each issued to Mowry) represent a family of related post-production video technology that seeks to arrive at an aesthetically acceptable simulation of the appearance that images originated on different motion picture film stocks would embody after telecine “flying spot scanner” transfer to video from taped high definition video originated images. One component of this prior art technology deals with the conversion of the video-originated material through a LUT that is based on color temperature of the scene lighting, scene brightness and selected f-stop setting. The conversion values in the LUT are derived by filming color charts and grey scale charts, obtaining a digital representation of the film component responses of the charts from telecine transfer of the film to videotape, and then charting the telecine-derived component responses against video originated images of the same charts under identical lighting conditions. Another component of this prior art technology allows for physically instilling selected film grain patterns to the video images. The final simulated video image is either recorded as a high definition signal, or converted to an NTSC signal and broadcast or displayed.
In the latter two of the aforementioned Mowry patents, the digitized video signal may be sent to a film recorder, which reproduces the component-modified images onto a selected, reversal film stock. The film is chemically processed with a film processor and then optically projected, or scanned to video, digital video, or other electronic media. However, if the film recording option is employed, these patents specify that it is important that the telecine-derived LUT used in the component modification involves response data which compensates for the inherent color response of the film stock on which the images are being digitally recorded.
Another prior art example of post-production digital image processing, which takes place outside the video camera or digital motion camera, exists in certain current image manipulation software packages. FIG. 1 shows a schematic diagram of one such example of this type of prior art processing, namely, histogram equalization. The histogram equalization method requires, for every frame 1 of a digital image that is to be manipulated, a scanned frame 2 of a reference film preferably with, for optimal results, the same scene content. Some resizing constraints 3 might also have to be met, depending on the software, because the digital image and the scanned film image will most likely not be the same size. Then, with these two input images, a well-known cumulative histogram equalization process 4 is performed to manipulate the electronically captured images closer to a film tonescale and color, thereby providing output manipulated images 5. This method, however, is not optimal because its inputs are of mixed formats: some form of RGB exposures from the electronically captured images versus the scanned film densities. As a result, it is impossible to optimally alter the tonescale and color of the electronically captured image to emulate scene exposure as seen by film.
Prior art also exists for generating a broadcast film appearance with video or digitally captured images, where the processing occurs inside of the camera. Specifically, setup cards have been described for beta-camcorders and also digital camcorders (see L. J. Thorpe et al, “The HDTV Camcorder and the March to Marketplace Realty”, SMPTE Journal, March 1998, pp. 164-177). These miniature plug-in setup cards facilitate prealignment of the camera to achieve an HD image having attributes similar to those that might otherwise be created from a film origination followed by telecine transfer to HD video. The setup cards can be pre-programmed to store desired digital data settings for aesthetic choices to be made concerning, among other characteristics, color reproduction, tonal reproduction and skin-tone detail.
In a combined approach, U.S. Pat. No. 5,319,465 describes a method using modified camera production and modified post-production processes and equipment to create filmic images. Specifically, the method includes the steps of shooting a benchmark comprising a gray scale chart, a color test chart and two backfocus charts with both a film and a video camera with comparable scene lighting and depth of field. Once the film test benchmark is shot, the film is transferred to videotape utilizing a telecine apparatus, with settings indicative of an industry standard set-up film. The video camera image's hue, saturation, luminance and gamma levels are manipulated to color correct the video camera image to look visually like the transferred film image. After the videotape has been edited, the videotape undergoes color correction in which the videotape benchmark is corrected to match the film test benchmark.
The prior art is generally trying to emulate the look of film after it has been telecine-transferred to video. This is desirable to some extent because the telecine system does have some film attributes when broadcasted. However, the prior art neglects the emulation of the look of film origination, as if a negative film has been directly printed and projected through a motion picture system. This is particularly desirable where the digital output is recorded on film for projection. Where the prior art does deal with film recording, as in the latter two of the above-mentioned Mowry patents, it does so in the context of a telecine-transferred benchmark. Moreover, when the prior art alters the tone scale and color of a video or digitally captured image to emulate a film, it is done on the telecine-transferred benchmark. This is an imperfect alteration because it cannot operate upon the scene exposure as seen by a film.
What is needed is a system that correctly emulates the look of film origination, particularly as to the emulation of film tonescale and color reproduction, as if a negative film has been directly printed and projected through a motion picture system.